Question

Is \[Mn{{\left( OH \right)}_{2}}\] soluble or insoluble in water?

Answer 1

Hint: We know that the solubility is the property of solute to dissolve in solvent. The solubility of the solute is related to the lattice energy. Less the energy required to separate in ions higher is the solubility of solute.

Complete answer:
The hydroxides of alkaline earth metals are less soluble in water as compared to the alkali earth metals. The solubility of hydroxides of alkaline earth metal depends on the lattice energy of the elements. The lattice enthalpies or the energies for a crystal is defined as the change in the energy when one mole of the crystal lattice is converted into the gaseous ions. In other words, the amount of energy required to break the crystal into its gaseous ions. Hydration enthalpy is the amount of energy released when one mole of the ion undergoes hydration.
It is a special case of solvation. The solubility of hydroxides of alkaline earth metal increases down the group. This is because lattice energy decreases down the group with increase in size whereas the hydration energy remains constant. This is because of the small size of ions. Solubility defines the ability of the substance or the ionic compound to dissolve in the solvent. Hydration energy or hydration enthalpy is the energy released when any one of the substances is undergoing hydration. Lattice energy is the energy required to break the bonds between the ionic compounds and convert one mole of the solid ionic compound into gaseous form. The lattice energy gives the strength of the bonds between the ions. Manganese (II) hydroxide, \[Mn{{\left( OH \right)}_{2}}\] is an inorganic compound which is insoluble in water.

Note:
 Remember that the atomic size increases, bond length increases and bond strength decreases which in turn makes the compound easily soluble in water. Higher the electropositivity and higher the electronegativity, more is the ionic character of the compound and greater will be its solubility in water.